mark Feature::RemoteControl as removed

[owenlin0]

Why

remote_control can appear in config.toml, CLI feature overrides, and the app-server config APIs. Before this PR, app-server startup treated config.features.enabled(Feature::RemoteControl) as the signal to start remote control (base code). That meant a user with:

[features]
remote_control = true

would accidentally opt every app-server process into remote control. Remote-control startup should instead be a per-process launch decision made by CLI flags.

What Changed

• Marks Feature::RemoteControl as Stage::Removed, keeping remote_control as a known compatibility key while making it config-inert.
• Adds a hidden --remote-control process flag to codex app-server and standalone codex-app-server.
• Plumbs that flag through AppServerRuntimeOptions.remote_control_enabled and makes app-server startup use only that runtime option to decide whether to start remote control.
• Removes the app-server config mutation hook that reloaded config and toggled remote control at runtime.
• Updates managed daemon spawning to use codex app-server --remote-control --listen unix:// instead of --enable remote_control.

Config APIs can still list, read, write, and set remote_control; those operations just no longer affect remote-control process enrollment.